SQL MERGE trying to duplicate update/insert. The insert/update is not ideal, but the sql merge hangs.

Question

I am trying to duplicate this update/insert with a sql merge:
-UPDATE [etag].Energy_Processed
SET Start_Datetime = estg.Start_Datetime,
--End_Datetime = estg.End_Datetime,
--Schedule_MW = estg.Schedule_MW,
--Active_MW = estg.Active_MW,
Load_Dt = GETUTCDATE() 
FROM  [etag].Energy_Stg estg, [etag].[Energy_Processed] ep
WHERE estg.Tag_Name IN
SELECT DISTINCT(tproc.Tag_Name) from [etag].[Energy_Processed] eproc
INNER JOIN [etag].[Tag_Processed] tproc ON tproc.Id = eproc.Tag_Id
INNER JOIN [etag].[Energy_Stg] estg1 ON estg1.Tag_Name = tproc.Tag_Name
           AND ep.Active_MW = estg.Active_MW
           AND ep.End_Datetime = estg.End_Datetime
          AND ep.Schedule_MW = estg.Schedule_MW 
INSERT into [etag].[Energy_Processed] (Tag_Id, Start_Datetime, End_Datetime, Schedule_MW, Active_MW, Load_Dt)
SELECT tproc.Id, estg.Start_Datetime, estg.End_Datetime, Schedule_MW, Active_MW, GETUTCDATE()  FROM [etag].[Energy_Stg] estg
INNER JOIN [etag].[Tag_Processed] tproc ON tproc.Tag_Name = estg.Tag_Name
WHERE estg.Id BETWEEN @minEId AND @maxEId AND
estg.Tag_Name NOT IN (
SELECT DISTINCT (tproc.Tag_Name) from [etag].[Energy_Processed] eproc
INNER JOIN [etag].[Tag_Processed] tproc ON tproc.Id = eproc.Tag_Id
INNER JOIN [etag].[Energy_Stg] estg1 ON estg1.Tag_Name = tproc.Tag_Name
SQL MERGE:
MERGE [Forecast_Data_Repository].[etag].[Energy_Archive] enArch
USING 
(SELECT ep.Tag_Id, ep.Start_Datetime, ep.End_Datetime, ep.Schedule_MW, ep.Active_MW, ep.Load_Dt 
FROM  [etag].[Energy_Stg] estg, [etag].[Energy_Processed] ep
WHERE estg.Tag_Name IN
SELECT DISTINCT(tproc.Tag_Name) from [etag].[Energy_Processed] eproc
INNER JOIN [etag].[Tag_Processed] tproc ON tproc.Id = eproc.Tag_Id
INNER JOIN [etag].[Energy_Stg] estg1 ON estg1.Tag_Name = tproc.Tag_Name
) AS sourceEP
ON EXISTS(SELECT sourceEP.Tag_Id)
WHEN MATCHED THEN
UPDATE
SET Tag_Id = sourceEP.Tag_Id,
Start_DateTime = sourceEP.Start_Datetime,
End_Datetime = sourceEP.End_Datetime,
Schedule_MW = sourceEP.Schedule_MW,
Load_dt = GETUTCDATE()
WHEN NOT MATCHED BY TARGET THEN
INSERT (Tag_Id, Start_Datetime, End_Datetime, Schedule_MW, Active_MW, Load_dt)
VALUES (sourceEP.Tag_Id, sourceEP.Start_Datetime, sourceEP.End_Datetime, sourceEP.Schedule_MW,
sourceEP.Active_MW, GETUTCDATE())
OUTPUT
$action,
INSERTED.Tag_Id
--UPDATED.Tag_Name
INTO @MergeOutput;
Greg Hanson

Answer 1

This bit
    ON EXISTS(SELECT sourceEP.Tag_Id)
Looks wrong. Sould be something like:
   ON sourceEP.Tag_Id = enArch.Tag_Id
And don't update the matching columns in the UPDATE part, as they already match.
David
David http://blogs.msdn.com/b/dbrowne/